Mf. Lachman, FIELD-MEASUREMENTS OF TRANSFORMER SINGLE-PHASE EXCITING CURRENT AS A DIAGNOSTIC-TOOL, AND INFLUENCE OF LOAD TAP CHANGERS, IEEE transactions on power delivery, 9(3), 1994, pp. 1466-1475
The single-phase exciting-current test can be used to detect undesirab
le conditions in single- and three-phase transformers. Normally the te
st results are analyzed by comparing currents between all three phases
in a given transformer and between the similar single-phase units. Ce
rtain problems, however, can be detected on the basis of current chang
e when the measurements are performed on different load tap changer po
sitions. Accordingly, understanding how the load tap changer affects t
he current magnitude of individual phases is essential for developing
proper analysis. This paper identifies twelve patterns of test result
behavior, and an attempt is made to show different load-tap-changer de
signs as they affect the measurement. The test results and test circui
t diagrams are given. The derived patterns will be implemented in a DO
S-based expert system in combination with a data acquisition system wh
ich is currently used in the field by more than 80 utilities.